Brassica napus is grown commercially to produce edible oil that is low in saturated fat. In Europe, B. napus is commonly referred to as rapeseed or rape. Most B. napus commercially produced in North America is canola, which by definition must produce seed that yields oil having less than 2% erucic acid and meal that contains no more than 30 micromoles of the following glucosinolates per gram of air-dry, oil-free solid: 3-butenyl glucosinolate, 4-pentenyl glucosinolate, 2-hydroxy-3 butenyl glucosinolate, and 2-hydroxy-4-pentenyl glucosinolate. As used herein, a “non-canola” B. napus line is one which does not meet this definition, e.g., because the seeds produce oil with too much erucic acid or have too high a glucosinolate level.
Most B. napus lines are typically classified as either spring lines or winter lines. Winter lines are commonly planted in the autumn and flower in the spring after a period of vernalization over the winter. Spring lines do not require vernalization to flower and are commonly planted and harvested in the same growing season. Winter lines are common in Europe, but most winter lines fare poorly in the colder winters of Canada and the northern United States. As a consequence, most B. napus grown commercially in North America are spring lines.
Although open-pollinated B. napus lines remain quite common, commercial production of spring B. napus increasingly employs hybrid lines. Hybrid lines tend to have higher yields due to heterosis or “hybrid vigor”. This heterosis is more pronounced the more distant the genetic relationship between the parent B. napus lines.
For this reason, several researchers have suggested crossing winter and spring B. napus lines to produce higher-yielding hybrids. For example, U.S. Pat. No. 6,069,302 (“Osborn”, the entirety of which is incorporated herein by reference) proposes crossing a spring B. napus line with a B. napus line that is itself derived from at least one winter line.